1. Field of the Invention
The present invention relates to configurations of solar cell array for solar electric power generation apparatus.
2. Related Background Art
Today, the increase in consciousness about the global environments is raising great hopes for the solar electric power generation apparatus as a clean energy source. In recent years, solar power generation-system interconnection devices for ordinary houses have become cheaper than before and still greater spread of solar power generation apparatus is expected in the future.
In constructing the solar power generation apparatus, solar cell strings are composed of solar cell modules connected in series so as to obtain a desired voltage, according to characteristics of the solar cell modules, and the solar cell strings are then connected in parallel so as to obtain a desired output capacity, thus composing a solar cell array.
In the system interconnection device, a selectable range of series number of solar cell modules is determined depending upon an input voltage into a system interconnection inverter, which is a receiver of the output from the solar cells. On the other hand, the maximum installation number of solar cell modules that can be installed is determined from the area of the place where the solar cells are installed, whereby the output capacity of the highest possible installation number of solar cells is also determined. Based thereon, the number A of series solar cell modules and the number B of parallel solar cell strings are determined so as to obtain a desired capacity, thereby constituting the solar cell array of A In series.times.B parallel strings of cells. Conventionally, it was common practice that the number A of solar cell modules composing each string was save for the all strings, so as to make the rated voltages of the respective solar cell strings equal to each other.
(1) For example, let us consider an example of installation on a roof where 51 solar cell modules can be installed as shown in FIGS. 6A and 6B. Let us suppose that the selectable number of series modules is in the range of 9 to 15 from the input voltage range of the inverter and the characteristics of the solar cell modules. The number of solar cell modules that can be installed in practice is one the multiples of 9, 10, 11, 12, 13, 14, or 15, but not to be more than 51. From this, the maximum installation number of solar cell modules is 50 and placement thereof is, for example, as shown in FIG. 6A. Solar cell strings 151, 152, 153, 154, 155 are constructed each by connecting 10 solar cell modules in series and these five solar cell strings are connected in parallel, thereby composing the solar cell array. A dummy module 4 is installed in a vacant area of the size of one solar cell module.
(2) Let us consider another example of installation in which the solar cell modules are installed on a south surface, an east surface, and a west surface of a roof as shown in FIG. 8. The solar cell modules used are building-material-incorporated solar cell modules SR-02 available from CANON Inc., and they are installed by the Dutch-lap method. The highest possible installation number of solar cell modules on each roof surface is determined depending upon the shape of roof surface and the above roofing method of modules; 73 modules on the mount plane A of the south surface; 14 modules on the mount plane B of the east surface; 14 modules on the mount plane C of the west surface. Supposing the inverter SI-04 available from CANON Inc. is used, the selectable number of series solar cell modules will be in the range of 10 to 20 from the input voltage range of the inverter and the characteristics of the solar cell modules. The number of solar cell modules that can be installed in practice on each roof surface is a multiples of some number between 10 and 20, inclusive. the configuration of 14 cells in series.times.5 parallel strings (solar cell strings 11' to 15') achieves the maximum installation number on the south surface, so that 70 modules can be installed on the south surface. In the case of the east surface and the west surface, the configuration of 14 in series.times.1 string (16', 17') achieves the maximum installation number, so that 14 modules can be installed on each of the east surface and the west surface. The total system is the configuration of 14 series.times.7 parallel string. There are three vacant areas 18 without a solar cell module on the south surface, and dummy modules are installed therein.
Another construction method of apparatus is a method for forming separate configurations of solar cell arrays on the respective mount planes and preparing an inverter per solar cell array. For the south surface, one solar cell array is constructed in the configuration of 18 series.times.4 parallel and one inverter is connected thereto. For either of the east surface and the west surface, an array can be constructed in the configuration of a solar cell string of 14 series, and they are combined to form a solar cell array of 14 series.times.2 parallel, to be connected to another inverter. In this way the two solar cell arrays are constructed and are connected to the respective inverters.
In the above construction method, the solar cell array formed on the east surface and the west surface can be changed to separate solar cell arrays, each on the corresponding roof surface. In this case, inverters for the east surface and for the west surface are prepared and are connected each to the associated solar cell array. Namely, the three solar cell arrays are constructed and the inverters are connected to the respective arrays.
However, the above methods have the following problems. Even if the output from the solar cells was desired to be maximized by installing as many solar cells as possible, there sometimes occurred such cases as to fail to utilize the all possible installation surfaces, because the conventional methods equaled the rated outputs of the respective solar cell strings or because the conventional methods equaled the numbers of solar cell modules forming the strings. In the aforementioned conventional example (1), though there are possible installation locations for 51 solar cell modules, only 50 modules can be installed owing to the array configuration and one position module cannot be utilized. In the aforementioned conventional example (2), though there are the possible installation locations for 73 solar cell modules on the south surface, only 70 modules out thereof can be installed owing to the array configuration and three rest modules cannot be installed.
With use of roof-material-incorporated solar cell modules, a dummy module having the same shape as the solar cell modules and incorporating no solar cell is installed as a roof material in each vacant module space, and the dummy module sometimes has a different tone of color, which is not preferable in terms of the design of the roof. In the case of the solar cell modules without the function of flashing, the dummy modules do not always have to be installed, but leaving a vacancy also is considerably undesirable in terms of the design.
In the conventional example (1), it is also possible to install 48 solar cell modules, as shown in FIG. 6B, giving a first priority to considerations of design in choosing among the possible installation numbers. In this case, however, the installation number is three smaller than the number of mountable locations, so that the output capacity is decreased further.
There are roofs in which the shape of mount plane is not rectangular; for example, a trapezoid like a hipped roof. In this case, since output terminals of solar cell string are not located at the edge of mount plane, wiring is not easy to find and the wiring work becomes troublesome.
In the case of the conventional example (2) where the plurality of solar cell arrays are constructed and the plural inverters are connected to the respective arrays, the extra inverter is necessary and the cost becomes higher thereby. If the output capacity of solar cell array is considerably smaller than the inverter capacity, the conversion efficiency of inverter will be lowered to decrease the electric energy obtained.
An object of the present invention is to provide a solar cell array that allows the maximum output capacity of solar cell array to be designed in the possible installation area of solar cell, that gives high degrees of freedom of design to permit a configuration preferred in terms of the design, and that is constructed in the device structure of low cost. Another object of the present invention is to provide an array construction method to facilitate installation and wiring.